Most modern homes are equipped with ventilation systems for heating and cooling, and these systems allow air to be exhausted to the exterior of the home. Such ventilation systems allow the home to be cooled in the summer and warmed in the winter. While this is pleasing to the occupants, vertebrate wildlife such as squirrels may also prefer to be cooler in summer and warmer in winter, and the ducts can provide an attractive nesting space.
As a result, it has been known to place mesh screens or molded plastic covers over the external vents in an effort to exclude vertebrate wildlife. However, squirrels, being industrious critters, are often not thwarted by such devices, and have been known to chew through or otherwise defeat such vent covers. While this leads to a comfortable home for the squirrel or other vertebrate, it is less so for the residents of the dwelling, as the unwanted animal guests may chew on wiring or cause other damage.